1. Field of the Invention
This invention relates to an artificial intraocular lens for implantation in the posterior chamber of the eye to obviate aphakia, the lens including retaining means, and further relates to instruments for implanting and removing the artificial intraocular lens, including respectively attaching and detaching the retaining means.
2. Prior Art
When no lens is present in the eye, which is known as the aphakic condition or aphakia and is usually the result of intracapsular or extracapsular lens extraction, the eye does not have the ability to focus rays of light. Therefore, the eye receives a blurred image and vision is impaired.
The most common solution for providing a focusing mechanism to obviate the aphakic condition is to interpose contact lenses or spectacles or a combination thereof between the eye and the light entering therein. However, both contact lenses and spectacles have drawbacks when used in the treatment of aphakia. Neither spectacles nor contact lenses can duplicate the natural optical system because they are positioned outside of the eye, which results in a shift of the optical center from the in vivo state. Because the optical center has been shifted, the image received by the eye is either distorted and/or changed in size. In particular, spectacles and/or contact lenses usually cannot be used to restore exactly binocular vision after removal or loss of the lens from one eye when the other eye continues to function normally.
Further, the most common reason for removal of a lens is the condition of lenticular opacity known as a cataract, which occurs primarily in aged persons who have difficulty in adjusting to contact lenses and in manipulating the contact lenses for insertion and removal. Cataracts are also common in animals, such as dogs and horses, and contact lenses and/or spectacles are not suitable devices for their treatment.
The desirability of implanting an artificial lens within the eye to obviate the condition of aphakia is well-known and accepted in countries such as England, Holland and Italy. However, practical devices for carrying out this desirable objective have not been perfected, although several devices have been used with a modicum of success.
In approximately 1950 Harold Ridley developed an artificial intraocular lens which comprised an optical lens portion having three foot-like projections or "feet" extending radially outward therefrom. Ridley originally placed this lens in the posterior chamber of the eye, behind the iris, with the feet resting against the ciliary body between the ciliary process and the base of the iris. However, positioning of this lens in the posterior chamber was abandoned because of instances of dislocation after implantation and failures from glaucoma and the like, probably caused by irritation of the ciliary body by the feet.
Ridley's failure with posterior chamber artificial lenses led him and others, such as D. P. Choyce, to turn their attention to intraocular artificial lenses implanted in the anterior chamber of the eye between the iris and the cornea. The particular lens used was similar to Ridley's original lens, and had radially protruding feet which accomplished positioning of the lens in front of the pupil. These efforts also met with limited success, primarily because of the problems of irritation of the eye by the supporting feet and dislocation of the lens from its desired position in front of the pupil.
It should be noted that placement of the lens in the anterior chamber is an unnatural position, with the attendant problems of restoring accurate binocular vision. Also, an anterior chamber lens is not positioned adjacent to the hyaloid membrance for supporting the vitreous humor, and instances of forward displacement of the vitreous humor and retinal detachment are more likely to occur when anterior chamber lenses are used.
E. Epstein and C. D. Binkhorst developed artificial intraocular lenses which rely on the constrictor muscle of the iris as the positioning mechanism. Eppstein first designed a "collar-stud" implant, with the pupil constricted in its waist for positioning thereof. Copeland's "Maltese Cross" pupil-supported implant has two leaves anterior to the iris and two leaves at right angles to the others and behind the iris. Binkhorst developed an iridocapsular (two-loop) lens and an iris-clip (four-loop) lens. The former comprises a lens of larger diameter than the pupil and placed thereover so that the periphery engages the front of the iris, and further comprises two metal loops which protrude from the back of the lens and extend generally parallel with the back surface of the lens and behind the iris for clipping the lens to the iris. Binkhorst's iris-clip lens is similar except that the iris is held by two pairs of loops which flank the iris and support the lens in front of the pupil. In some instances, the iris is sutured to the clips to secure the positioning of the lens. This type of lens is also unsatisfactory in several respects. It, by necessity, interferes with constriction of the pupil, and in fact fixes the size of the pupil. It is also an anterior chamber lens, wherein correct positioning of the optical center cannot be achieved.
J. G. F. Worst considered posterior placement of an artificial lens to be desirable, but developed a lens having a pair of closely spaced openings for positioning in front of the iris. A suture was placed through the two openings and attached the lens to the iris. Although it is not believed that Worst's suture would cause irritation of the ciliary body, as did the earlier posterior lens of Ridley, the difficulty of the technique necessary to suture the lens in position without damaging the iris as well as the possibility that the suture would not hold or would tear out from the iris has limited the acceptance of Worst's lens.
Additional artificial lenses designed for positioning in the posterior chamber are described in U.S. Pat. No. 3,711,870 to Deitrick and in U.S. Pat. No. 3,673,616 to Fedorov et al. Deitrick's lens comprises a central optical portion surrounded by a resilient silicone flange shaped to receive and nest against the ciliary body. The lens is to be held in place by suturing the resilient flange to the ciliary body. Although the medical worth of the Deitrick lens is not yet known, it is known that it would be difficult to place sutures where Deitrick directs and it is also known the there may be reluctance on the part of ophthalmologists or ophthalmologic surgeons to do so because of the many risks attendant with the irritation of the ciliary body. Fedorov et al's lens is supported in the eye by radially protruding prongs flanking the iris and gripped by the constrictor muscles of the iris adjacent to the pupil, in somewhat the same manner as the Binkhorst lens.
Several of the prior art lenses are discussed in an article by D. P. Choyce entitled "History of Intraocular Implants" which is printed in Annals of Ophthalmology, October, 1973. The article also includes a list of references from which further information concerning prior art intraocular lenses can be obtained.
Several of the above lenses rely on sutures placed in the iris for holding the lenses in position. It should be noted that the iris consists of spongy, flexible tissue which may be pulled and stretched to a limited degree without damaging it. However, the iris has the unique property of never healing together after being cut or damaged. Thus, if a suture pulls through the iris, the damage to the iris is permanent. Because sutures are generally of a small diameter, if a lens positioned and held by sutures is subjected to a dislocating force, the sutures may cut the iris, resulting in permanent damage.